The number of echoes combined into a single image or image set in multiple echo imaging sequences or echo-train techniques such as rapid acquisition with relaxation enhancement (RARE), fast-spin echo (FSE), and turbo spin-echo (TSE). In RARE imaging, the ETL typically equals the acceleration factor.
As for tooth pain, it is caused by a reaction of the nerves inside a tooth's pulp chamber with the severity dependent upon the type and degree of the stimulus. What follows are some examples of symptoms you may be feeling and their possible causes.
Toothache Overview. A toothache or tooth pain is caused when the nerve in the root of a tooth or surrounding a tooth is irritated. Dental (tooth) infection, decay, injury, or loss of a tooth are the most common causes of dental pain. Pain may also occur after an extraction (tooth is pulled out).